The present invention relates to injection-molding machines and in particular to the automatic removal of injection-molded workpieces from multicavity molds.
In many injection molding machines, articles molded in an injection cycle are discharged from the movable mold portion as it approaches its withdrawn position, generally with the aid of one or more ejector rods or pins which enter each cavity of the receding mold portion and dislodge the respective workpiece therefrom. The workpiece then falls between the mold portions into a suitable receptacle disposed underneath. With molding machines operating at ever-increasing speeds, such injection systems are no longer satisfactory because the discharged workpiece may not drop rapidly enough to clear the path of the reciprocating mold portion.
Numerous attempt have been made to provide a device for rapidly removing workpieces from the mold during the operating cycle. U.S. Pat. No. 3,454,991 to Rees shows an expandable device attached to a cam operated arm which unloads a container shaped part from its mold cavity. The arm is moved by the action of the mold clamping mechanism so that no cycle time is lost. A second embodiment in this patent shows a cam operated arm extending between the mold halves. The arm carries a recessed cup in which the ejected part is carried. U.S. Pat. No. 3,700,375 to Rees shows a vacuum suction head mounted on a cam operated arm for removing a workpiece.
U.S. Pat. Nos. 3,729,103 and 3,804,568, both to Rees, show a two stage approach where a cam operated take-off plate enters the mold area from above and picks up parts from several mold cavities. Thereafter, it moves to an outboard position where the parts are transferred to a second handling device which is cantilevered on a transverse shaft at the top of a column rotatable through 180.degree..
U.S. Pat. No. 4,204,824 to Paradis exemplifies another device for facilitating the removal of molded structures from mold cavities at the end of each molding cycle. The removal mechanism comprises a rack and pinion driven arm whose movement is coordinated with the opening and closing of the molding machine. The removal member is slidable or rollable on a header or mount which is in turn slidable or rollable with respect to a transverse rack.
U.S. Pat. No. 4,212,622 to Kikuchi et al shows a floor mounted robot having an extensible arm for reaching into an open mold and removing the part. The arm is controlled by a cam-operated four-arm linkage assembly. U.S. Pat. No. 4,795,124 to Nagai illustrates a pivoting tool arm for parts removal.
These devices currently have no utility in stack mold arrangements. They would be extremely cumbersome and complicated when modified for use with stack molds. Additionally, some were developed for use with the small strokes and short travel distances found on single cavity molds.
There exists a second group of devices which maintain workpiece orientation after the workpiece is removed from the mold. These devices are illustrated in U.S. Pat. Nos. 3,408,689 to Heiner, 3,910,740 to Rees, 4,157,888 to Sikorski and 4,589,840 to Schad.
The Heiner patent relates to a multi-receptacle conveyor and discharge apparatus for carrying molded parts from a mold station to a discharge station. The apparatus is characterized by an assembly comprising a plate having a plurality of openings and a relatively movable shutter underlying the plate and movable relative thereto. The shutter blocks the openings when the plate is moved toward the mold station whereby segregated parts stripped from the mold are individually received in and held segregated in the blocked openings. It moves to allow the segregated parts to drop through the openings into separate part storage containers when the plate is moved to the discharge station.
The Rees '740 and Sikorski patents both show a mold mounted guide rail system for guiding ejected workpieces away from a mold area. The rails are moved by cams activated by the clamp drive mechanism and without causing a loss of cycle time.
The Schad patent also shows a guide chute system for removing air ejected parts from a stack mold. The chutes are moved by cams actuated by the clamp drive mechanism without penalizing the cycle. The chutes carry a vacuum means for catching the ejected parts and do not require the precise ejection alignment control of the guide rails.
The guide rail approach shown in these patents works well with shallow parts such as lids which are ejected into precisely held locations. This approach however is not suitable for handling deeper air ejected parts.
Some guide chute designs suffer from two major disadvantages. First, they require considerable additional space between the mold tiebars to accommodate the chutes in the outboard position. As a consequence, a machine having a larger platen area than otherwise would be necessary must be used. Second, the air ejected parts are not always reliably captured by the vacuum system in the chutes. The ejected parts tend to drop slightly before they are caught and may consequently hang up during ejection.
Accordingly, it is an object of the present invention to provide an improved device for removing workpieces from an injection molding machine.
It is a further object of the present invention to provide a device as above which enables the space between the molding machine tiebars to be minimized for a given part height.
It is yet a further object of the present invention to provide a device having more standardized components than other devices.
It is still a further object of the present invention to provide a device as above having particular utility in stack mold machines.
These and further objects and advantages will become more apparent from the following description and drawings in which like reference numerals depict like elements.